text:
Did AF447 cross dangerous weather?
question
Did the Air France 447 pilots endanger the passengers by not diverting around but flying straight through the weather system encountered and pictured below ? Or was this a defendable, unproblematic choice ?
scope (judging from some answers, I'm obliged to clarify this): I'm NOT asking why AF447 crashed – this BEYOND the scope of this question, which solely asks about the meteorological conditions. What went wrong, went wrong INSIDE the storm cell. On the contrary, my question is about the decision BEFOREHAND whether or not to enter this particular storm cell pictured below. This question is entirely independent from the outcome (crash) and would have merit even if AF447 had not crashed.

meteorological and other background information:
Other flights on the same route chose to divert:

« Three other flights (IB6024 [A343, Rio De Janeiro GIG-Madrid MAD
  12 minutes behind AF-447], LH507 [B744, Sao Paulo GRU-Frankfurt
  FRA] 20 minutes behind AF-447, AF459 [A332, Sao Paulo GRU-Paris
  CDG 37 minutes behind AF-447]) tracked the same route to TASIL between
  FL350 and FL370 around the time of the crash. They all had to avoid
  storm cells and diverted from the airway between 11 and 80nm. They
  experienced moderate turbulence. All three flights had problems to
  establish communication with Dakar. » (source)

The french newspaper "Le Figaro" asked why AF447 flew through the thunderstorm when other flights diverted around it:

« I note Figaro's graphic borrows from the BEA interactive where
  one could see the routings of other planes that night. However, for
  reasons known only to the BEA, the BEA no longer references LH507
  which preceded AF447 along the UN873 airway by 20 minutes, nor (if I
  recall correctly) does the interactive include IB6024 which followed
  AF447 on UN873 by 12 minutes. Instead, the BEA interactive mostly
  plots flights on a parallel airway over a 100 NM distant. Both the LH
  and IB deviated off the track because of the weather, and one would
  think their deviations would be the most relevant to what AF447 did
  not do. » (source)

The weather encountered by AF447 is analyzed in detail here, here and here.
Weather infrared satellite image Meteosat-9:

Weather Satellite Infrared Image 02:45Z Jun 1st:

View of AF447 track using GOES imagery:

 Figure 12. Probable radar depiction (green/yellow/red
  shading) based on thermal signatures and conceptual MCS models. Units
  are arbitrary approximations of radar strength ranging from green
  (weak) to red (strong). This is based on careful enhancement of cloud
  temperature information. This is just an assumption of course but this
  is the best guess based on my own experience and the satellite
  signatures available.

note: I don't understand why the question gets downvoted. I'm neither claiming nor assuming or guessing that the choice to fly straight through the storm cell was problematic. I'm only asking because I honestly don't know. I'm neither a meteorologist nor a pilot, so forgive me for asking, because I am really curious about this aspect. I'll happily accept either conclusion.

Was that "obviously" dangerous, or "prohibited" legally or by Air France guidance? No. Was that more dangerous than calm air: Yes. Bypassing it has a price in dollars and in delay. As for everything in aviation, there is a balance to find, sometimes subjectively, specially in the ITCZ

You are saying there is a choice between $ and safety ?

Of course. Safety improvement has an exponential cost and cannot be total. You need to stop somewhere. I'll take the example of this. There have been deadly accidents with children inserting things in the holes. Now we have that (we must push on the two protections simultaneously to insert something). This has a price, and does decrease the accident rate. However with better, more expensive systems an engineer could decrease the rate further. This is not required by law, and not done, for economical reasons.

The pilots did discuss the weather ahead and made some corrections to their course to compensate:

25 minutes before the autopilot disconnected they discussed climbing to a higher altitude, but the temperature was too high for them to climb.
They turned on the landing lights and noted they were entering clouds and would be encountering some turbulence.
They noted the upcoming turbulence to the cabin crew.
They experienced light turbulence with a max of about 1.5 g’s, which is borderline moderate.
They slowed from 0.83 Mach to 0.80 Mach, which is the recommended turbulence penetration speed.
Two minutes before the autopilot disconnect they increased gain on the weather radar and adjusted course 12° left of their planned track.

They knew the weather was coming and made the adjustments that were available to them to get through it. Nothing indicated to them that it would be more problematic than turbulence. This turned out to be correct, since the most they experienced was light to moderate turbulence.
There is really nothing there to indicate that the weather they were flying through was anything that would be unsafe. There were other aircraft that flew through ahead of them, but they got no reports of dangerous weather. I think the images in your question make it appear worse than it really was. They did discuss the weather, but nothing they said on the CVR indicated that they expected it to be unsafe, just bumpy.
It boils down to opinion as to whether they were justified in flying through, but there really is nothing indicating that it was anything more than just a bumpy ride.

The question seems to overlook the facts of the pitot system icing up.

The BEA's final report, released at a news conference on 5 July 2012, concluded that the aircraft crashed after temporary inconsistencies between the airspeed measurements – likely due to the aircraft's pitot tubes being obstructed by ice crystals – caused the autopilot to disconnect, after which the crew reacted incorrectly and ultimately caused the aircraft to enter an aerodynamic stall, from which it did not recover.

It seems to me that you are playing up the weather aspect too much.

Weather conditions in the mid-Atlantic were normal for the time of year, and included a broad band of thunderstorms along the Intertropical Convergence Zone (ITCZ). A meteorological analysis of the area surrounding the flight path showed a mesoscale convective system extending to an altitude of around 50,000 feet (15,000 m) above the Atlantic Ocean before Flight 447 disappeared. During its final hour, Flight 447 encountered areas of light turbulence.
Commercial air transport crews routinely encounter this type of storm in this area. With the aircraft under the control of its automated systems, one of the main tasks occupying the cockpit crew was that of monitoring the progress of the flight through the ITCZ, using the on-board weather radar to avoid areas of significant turbulence.[82] Twelve other flights shared more or less the same route that Flight 447 was using at the time of the accident.

It seems to me that the younger pilots didn't do their job very well, allowing the aircraft nose to climb too high and stalling the airplane.

re: "you are playing up the weather aspect too much." I'm not "playing up" the weather aspect, I am focusing the question on this aspect, which – I hope you'll agree – is legitimate, right? I'm not playing up anything. You are misinterpreting the question by reading something into it, which just is not there. There is nothing to interpret – I'm just posing a question. I am not implying the answer to be "YES" at all. In fact, I don't know one way or the other. If I did, I wouldn't ask the question. You might want to rethink that personal comment, as it has no relevance for the answer.

The main effect of the weather aspect was to ramp up the stress level of the inexperienced flight crew.  The actual phenomenon that caused the airspeed fluctuations, thought to be ice crystals in the pitot lines, wasn't related to the weather itself and incidents have happened in "clear" air.  What killed the crew was inadequate basic instrument flight skills and poor situational awareness.  The right seater was in pure panic mode the entire ride down, and the left seater was too mentally saturated to think to override the right seater's panic mode full aft control inputs.

There's an old saying from the helicopter world... "don't just do something, sit there".   It means don't overreact.  A well trained IFR pilot, when he/she sees some  indication go bonkers when cruising along, will "just sit there" and evaluate.  Cross check other displays.  If the airspeed jumps but the attitude didn't change and you didn't feel any vertical motions, just leave things alone because you are probably still in level flight.  They reacted and got themselves disoriented instead of assessing, and the capt didn't intervene soon enough.  I'dve dragged the left seater out of his seat.

@JohnK I’m not defending his flying skills, but he couldn’t “just sit there.” The autopilot disconnected and it started banking. He had to hand fly. Why a qualified pilot was unable to hand fly and maintain straight and level flight for a minute or so while they worked the problem is the crux of the situation.

Good point, but still, if the AP kicks off and the airplane is banking, do the absolute minimum; level the wings, pitch attitude, assess.  All 3 airspeeds increasing, but all 3 pitch attitudes show level flight and no noise buildup, no altitude change?  They needed to be able to filter that information, but instead they quickly became disoriented.  If there is too much conflicting information, you have to ignore it all and drill in on something basic you can trust, like standby attitude.  Part of the problem is the type courses are as short as possible and can't possibly cover all scenarios.

It depends on what the crew was seeing on their own weather radar.  If they were seeing something like what the satellite imagery was depicting, a giant mega-cell, I would say yes, they were foolish to blunder through.  But they may have been seeing something more manageable or benign looking, such as individual cells with gaps, on their own radar.
Plus the seats were being occupied by the FO on the right and a fairly inexperienced relief pilot on the left, and their ability to interpret radar returns may have been limited.  One important factor here is the fact that attenuation of the signal from heavy rain can create black spaces beyond what appears to be the main area of the storm, which can entice pilots to that area thinking it is clear, when actually the black space is the real center of the cell.  Experienced pilots learn to interpret the returns keeping that effect in mind.
447 was a confluence of bad luck, bad decision making and some bad flying, with the key decision maker unable to directly intervene.  A pretty rare combination.

What "bad luck" ?

Capt being away when they had to make some key decisions.


text:
Why shoot down a passenger plane without knowing it will crash?
Flights threatened by a passenger and flights with lost coms and even flights in technical difficulty without criminal intent and not posing a security threat are sometimes intercepted and escorted by fighter jets.
One of the mentioned reasons is to shoot down the passenger aircraft if people on the ground are at risk.
I fail to understand the logic. It's impossible to know in advance where exactly and even if the plane will crash at all. Non-intervention may result in 0 deaths. Why kill hundreds of passengers when it's unclear they would die ?

You seem to be asking, "Is it ethically right to kill one group of people in order to protect another group of people?" That's an ethics question, not an aviation question.

No, it's a procedural question. I don't understand the logic of this aviation procedure. Also your quote is not what I am asking.

For me, this is a political and moral question, not an aviation one. Someone somewhere has to make the decision based on the specific situation, it isn't just a "procedure" to follow automatically. In any developed democracy, authorizing the military to kill civilians would be a hugely significant and controversial decision (and very possibly illegal). You might get a better response on politics.SE.

Sorry but I differ. Whether it's controversial or not does not change the fact that this is a question about a procedure squarely within the aviation world. It's in the same category as "What's the point of intercepting an aircraft?". Both questions are procedural and ask for an explanation of an aviation procedure they don't understand.

If you're still interested in receiving answers to this question, I recommend going to https://aviation.meta.stackexchange.com and asking for it to be reopened.

Also, which aviation procedure are you asking for an explanation of? If you're asking for an explanation of the procedure of intercepting an aircraft, then this question is a duplicate. If you're asking for an explanation of the procedure of shooting down a passenger aircraft, then I think the question is meaningless because there is no such procedure.

Most escorts are actually unarmed. Fighters don't sit around in their home country with armaments on board. That could lead to incidents like this.
Escorts are there primarily to provide eyes on the primary, attempt non-radio communication, and provide instant, reliable reports up the chain of command of anything that happens, such as course changes.
Escort planes also provide lights and squawks, so even if the primary turns off their lights and transponder, they still are not a threat to other air traffic navigation.
Shooting down a plane is an option, in the most extreme situations, but has never actually occurred.  Except for 9/11, I'm not sure a shootdown has ever even been seriously contemplated.  Even on 9/11, the planes closest to Flight 93 were unarmed, and would've been ordered to "kamikaze" it.

Both kill innocents, the killing method (shootdown or kamikaze) doesn't matter. And your first 3 paragraphs are not on topic (the question is about a shootdown).

His comments are exactly on topic.  You are presuming that the primary function of a fighter escort is to shoot down the civilian plane, and he is countering that assumption.

9/11 changed the entire paradigm related to hijackings. Before that any hijacking was assumed to be so and so wanting to force the plane to go somewhere, where they would get off, or collect a ransom or whatever.  It introduced the idea of airliners being turned into cruise missiles by suicidal hijackers to take out institutional structures.  The 9/11 airplane brought down by the pax in PA was thought headed for the White House.
This means that any hijacking is now assumed to be that sort of thing, instead of an excursion to Cuba.   Authorities now have to prioritize pax vs, say, a seat of government.  Seat of government wins.
It means also that on any hijacking in future, the pax are much more likely to intervene than in the old days, because they know they have nothing to lose.  That, and and introduction of reinforced cockpit doors and changes in access protocols has resulted in hijackings being pretty rare now.
When airplanes start going places where they are not supposed to, for unknown reasons, you have to assume the worst.  Hence fighter jets.

re: "you have to assume the worst" – Why kill innocent people on a mere assumption ?

Assume the worst relates to the practice of dispatching jets not the shoot down.  They don't just say, "looky there an airplane is off course and we don't know where it's going so blow it to smithereens just in case".  A bunch of people at a very high level, who are going to have to live with the decision for the rest of their lives, have to be satisfied that the balance of risk has crossed a line at some point.  If your jets had intercepted an airliner heading for WTC, and you and your experts and advisers had very high confidence that WTC was the target, what would be your choice?

As stated in the question "It's impossible to know in advance where and if and if the plane will crash at all". Both are only knowable ex post facto. Why kill innocent passengers when it's not completely uncertain they will die. I have not seen any explanation for that yet. I have made this point in another comment which fell pray to a user deleting his answer here. Maybe a moderator can restore my comment?

Also you say "Assume the worst relates to the practice of dispatching jets not the shoot down." but then you go on to say that the passengers should be shooted down when assuming the worst. That's my point. Why kill innocent people on a mere assumption. If it were a certainty, it would be ethically questionable. But killing innocents based on a assumption only is a procedure I just fail to understand logically.

Go back to the last line of my comment.  In view of the new paradigm of airliners as potential human cruise missiles, and an airliner has done something wild and crazy like break off contact, head for the deck, and is heading on a bee line to Capitol Hill, something no normal crew would do in a billion years, what choice do you make?

I already answered that: If and where a plane crashes is only knowable with certainty a posteriori. Why kill innocent people based on a speculation that can be false? The heading can be a coincidence. Or the crew could regain control. Or the plane could crash-land with half of the passengers surviving. There are so many possibilities.

@summerrain it's pretty clear where in a rough area the wreckage will fall when you shoot something down. Physics sees to that. Forward speed m/s, gravity 9.81 m/s2, you get a predictable parabolic arc.

@summerrain it's simple: the lives of the people on board that aircraft are worth X, the lives of those on the ground Y. If Y > X, you sacrifice those on board. Harsh, but that's the consideration. Determining X and Y are the hard part, and I'd not want to be in the shoes of those making that determination, but you can be assured there are documents detailing such decision making processes somewhere, and that the value of politicians is extremely high according to those documents.

It's only knowable ex post facto if and where a hijacker manages to crash the plane if it is not shot down before. And your calculation only makes sense if you know X or Y will die, which is not the case at all. You are missing the point. Why kill innocent civilians preemptively? It's not even certain anybody has to die.

@summerrain Yes there are many possibilities of how such a scenario might turn out - but they aren't all equally likely. If the most likely outcome of not intervening is that the plane will be intentionally crashed into a population center killing Y people (plus the X people on board) then preemptively shooting the plane down and "only" losing X lives (rather than X + Y) starts to make a whole lot of sense.

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sort: votes


text:
Why are waypoints not named uniquely?
Waypoint names are not unique. Why ?

This is unnecessary (it would be possible to use unique names only).
It introduces potential for confusion.

So why are duplicate waypoint names permissible and used ?
I don't see a good reason for that.

They sometimes get creative to avoid this problem. There are several examples around the US, at least.  Check the COMIX TWO ARRIVAL into San Diego (KSAN.) They try their best to separate identical names as far as feasible.

ICAO does actually recommend that names for significant points are unique:

3.4 The   unique   five-letter   pronounceable   name-code designator assigned to a significant point shall not be assigned to any other significant point.

However, as you already know, not all names are in fact unique. So why is that?

This is unnecessary (it would be possible to use unique names only).

No, it probably wouldn't. There are millions of named significant points around the world. Assuming points could be named completely randomly (any combination of 5 letters), just about 12 million unique names would be available (26 to the power of 5). However, points are not just named randomly, they have to follow some rules:

3.2 The  name-code  designator  shall  be  selected  so  as  to avoid   any   difficulties   in   pronunciation   by   pilots   or   ATS personnel   when   speaking   in   the   language   used   in   ATS communications.
3.3 The   name-code   designator   shall   be   easily   recognizable   in   voice   communications   and   shall   be   free   of ambiguity  with  those  used  for  other  significant  points  in  the same general area.

You can't just put together 5 letters in a unique way, you have to create a pronounceable, recognizable word, and it can't sound similar to other points in the same area. This significantly limits the number of options.

It introduces potential for confusion.

In theory, yes. In practice, this is not a problem. The risk of pilots navigating to a point with a duplicate name is next to none. Points with duplicate names are never located in close proximity, and most flight management systems will automatically select the nearest point, when inputting a route where duplicates exist. I'm not saying a mishap related to this issue has never happened in the history of aviation, but personally I have never heard of one, and I doubt I ever will.
All references from ICAO Annex 11, Appendix 2

Waypoints do not have to have unique names as long as they are separated by enough distance so that confusion over names would be highly unlikely.

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text:
What are the differences between the two main brace positions?

Why are there two different brace positions (pictured below) ?
(If there is a difference between the official and true reason, please state both. In many planes the reduced seating spacing does not allow the pike position (on the right), but I doubt this is the official statement of airlines.)
Are they equally protective ? If not, why are both recommended ?
What arguments are there in favor or against each ?
If available, statistical data and relevant links to studies and crash tests would be very welcome if they distinguish between the two positions.

We have answers on that here and here. Please explain what those two answers leave unclear.

They don't answer any of the questions above.

No. Q12599 is a different question. It is not about the pike position, but about the head-against-seat-in-front-of-you-position and only asks about the arm position in that case. Please remove the comment. Thank you.

The semi-upright position is the only position available for my portly self.  I can't breathe in the pike position. Perhaps the growing girth in the general population comes into play on the choice of prayer position before the crash.

One is for when the seat in front of you is in the way of using the other.
The other is for when you can't reach a seat in front of you.
They won't both be relevant for the same person in a given seat. If you can assume the second position, the first one probably won't provide meaningful support for your head anyway.

The most useful brace position is when you place your head right down between your legs and kiss your a** goodbye. hardeharhar

Thanks. This partly answers the question. Remaining questions are: Which of the two is more protective and why? And what reason do airlines give for the existance of 2 positions? I very much doubt they say "our seats are so close that you cannot use the safer position" ...

@summerrain You're assuming that one (specifically the "pike") is automatically "safer" than the other. That isn't necessarily true: in the alternative position, the head is supported by the seat in front -- maybe that's actually beneficial.

Yes, I assume one is more protective but not which one. I'm just saying IF it's the pike, the official airline statement won't be "our seats are too close for the safer position". But regardless of the merits of either position, I am curious about what reason airlines state for the existance of 2 different positions. I have never heard them say that seat spacing is insufficient. That's not the reason they give. I'll happily stand corrected if provided with such a statement.

I can't recall an airline ever giving a reason; it's assumed you'll do whichever one matches your body size and available space; there isn't really a choice for any given passenger anyway.

@summerrain, if you were airborne facing this situation and didn't have your laptop to pose the question, which position would you select - and why?


text:
How to increase your chances of survival in a plane crash?

More than 90% of plane crashes in recent years had survivors.
In America, for example, there were 568 plane crashes between
  1983 - 2000:   Out of the collective 53487 people onboard, 51207 lived
  to tell the tale. That's a survival rate of 96%.
Some experts believe that almost one-third of deaths in aeroplane
  accidents could have been prevented if people knew what to do and took
  action. (source)

Question:
Beyond bringing on board special items, what are the things a passenger can do to increase his chances of survival in the unlikely event of a plane crash – including its aftermath ?

note: Although plane crashes are very rare, it's nevertheless a question worthy of contemplation both
– theoretically, for argument's sake, as it's an interesting thought all by itself
– and from the point of view that each preventible human death is one too many and unnecessary. For the tens of thousands who experienced a crash as well as their friends and relatives it's certainly not a theoretical question.

To me this looks off-topic, being directed to passengers.

It's in the same category as Q556 though.

that has been asked 5 years ago in the early days of the site, when the scope had not yet been fully worked out. I would rise the point on meta

It would have to be closed now though. Along with lots of questions about the brace position for example. Is that really what we want?

Best thing to do is not worry about it, the odds are high you will never be in a crash.

« Some of the survival game involves factors passengers largely can't
  control, like the weather, flight crew skills, the design of airline
  seats and the construction, maintenance and age of the plane. But
  passengers themselves can do a lot to improve their chances of
  survival simply by making smart choices and being informed. »⁴

Things you can do:
Preventive Measures

Book the safest seat.
Avoid unsafe airlines.
Fly during daytime (as statistically it slightly increases chances of survival and some kind of incidents are far more common at night).

Preparatory Measures

Bring helpful items on board.
Clothes – what you choose to wear can help or hinder your escape:

Opt for flat, sturdy shoes. Flip-flops and high heels won't help you make it to the emergency exit.²
In case of a fire or glass and metal debris, long-sleeved shirts and heavy cotton trousers will offer more protection than shorts and a T-shirt.²
Form fitting clothes are less prone to catch fire.
Polyester and other synthetic fabrics will melt to your skin.³

Before Take-Off

Pay attention to safety advice. It can save your life. Read the safety card (in the seatback in front of you) as planes do differ.
Memorize the emergency exit locations before take-off. Plan and visualize your escape route. Count the rows (armrests⁴) to your nearest exit (in front of and behind you in case one direction is blocked!). That way, in the event of smoke filling the cabin or if emergency lighting fails and it’s very dark, you will know the number of seat rows and can feel your way to an exit.¹ Many passengers survive the initial impact but are killed by the ensuing fire, smoke and sometimes water. 90 seconds should be used as a time frame for escaping.⁴
Memorize where your nearest cabin crew are, because their help and instructions will make a huge difference.²
Be aware that at 35000ft you have just 30-60 seconds to don the oxygen mask and tug on the line to get the flow going. After that, you lose consciousness.²

In-Flight

Don't drink alcohol.
Seatbelt:

Keep your seatbelt on whenever seated (also prevents turbulence deaths).
Fasten it tightly - every inch of slack increase the potential g-forces you could be subjected to during an impact.²
Wear it across your pelvis, which will handle impact better than your stomach².
Practice opening and closing it:

After interviewing 1,900 survivors and 155 cabin-crew members,
  Professor Galea made an interesting discovery: Most passengers lose
  valuable time because they struggle to undo their seatbelts. “People
  tend to try and press a button on the seatbelt, because in this
  emergency situation they revert to normal behaviour [learned from] car
  seatbelts [with] a push-button system.”²

During Take-Off and Landing (when ~80% of accidents occur²):

Don't sleep/nap wearing eye mask and earphones.²
Stay alert and aware of your surroundings.²
Keep your shoes on.²

When a Crash is Imminent

Brace for impact:

Put your feet flat on the floor, farther back than your knees ("aft position").²
Consider placing hand luggage under the seat in front of you to act as a cushion (to prevent your feet from hitting the seat, I assume). That way you are less likely to suffer broken ankles that will hinder your escape.²

Escape and Aftermath

After the initial impact it's common for fire to break out. Just a few breaths of toxic smoke can cause you to pass out. In the event of smoke/fire:

Cover your mouth and nose with a wet cloth (e.g. wet the seat back headrest).²
Stay low. (That doesn't necessarily mean crawl on your hands and knees. Although there will be less smoke at floor level, you could be crushed or suffocated under luggage and other passengers.) Instead, keep your head down.²

Don't retrieve your luggage.¹
Don't inflate your life jacket inside the plane. It hinders your escape.²
Move fast but resist the urge to push and shove. It's likely to make matters worse and cause others to lash out.²
Once on the ground get away as fast and as far as you can.²

sources: 1, 2, 3, 4


text:
Which underwater crash sites of medium to large aircraft have been captured in sonar imagery?
For which crash sites of medium to large aircraft are sonar images available ?
Scope:

The crash site should already be confirmed (not speculated).
For the purpose of this question, let's define "medium to large" as aircraft seating at least 10 persons or an at least equally sized cargo aircraft. This excludes small aircraft, like World War fighter planes for which sonar images exist by the dozen.

Below are the only cases I was able to find. If you you know other cases (or can provide the missing images below), please include the images in your answers if possible.

Air France flight AF447
• 228 occupants, Airbus A330-203, lost:2009, found:2011, depth:3980m
• location: mid Atlantic Ocean
see paper "AF447 Underwater Search and Recovery Operations" (pages 6+14)

EgyptAir flight EA990/MS990
• 217 occupants, Boeing 767-366ER, lost+found:1999
• location: Atlantic Ocean, 100 km south of Nantucket
see article: "Pilot Suicide: When It's The Captain Who Crashes The Plane"

EgyptAir flight EA804/MS804
• 66 occupants, Airbus A320-232, lost+found:2016, depth:3000m
• location: offshore Egypt [avherald]
I couldn’t find any publicly available sonar images of this crash site, but some must exist, because Deep Ocean Search (DOS) wrote here:

« With the agreement of the Egyptian Civil Aviation Authority and the French Safety Investigation Authority (BEA), DOS have supplied the
Australian Transport Safety Bureau (ATSB) with side scan sonar data
of the MS804 crash site in order to assist with the on-going MH370
search. »

In a press release, DOS explains:

« At this moment, DOS ltd is not authorized to supply any pictures, videos, chart and/or positions linked with the investigation. »

Indian Air Force An-32 crash
• 29 occupants, Antonov An-32, lost:2016, found:2024, depth:3400m
• location: Indian Ocean, off the coast of Chennai (India)
Again, I was unable to find sonar images of the crash site, but some do exist (maybe not in the public domain since it is a military aircraft):

« This search was conducted at a depth of 3,400 metres using multiple payloads, including a multi-beam SONAR (Sound Navigation and Ranging)
— a synthetic aperture SONAR and high resolution photography.
Analysis of search images had indicated the presence of debris of a crashed aircraft on the sea bed approximately 140 nautical miles
(approximately 310 km) from the Chennai coast, the IAF said in a
statement. It added that the search images were scrutinised and found
to be conforming with an An-32 aircraft. » sources: 1 2

South African Airways Flight SA295/SAA295
• 159 occupants, Boeing 747-244BM Combi, lost:1987, found:1988, depth:4400m
• location: near Mauritius
I couldn't find any sonar images. Allegedly sonar images are presented in the "Mayday" televised series, but they could be just illustrative examples rather than the original images.

Flash Airlines flight FSH604
• 148 occupants, Boeing 737-3Q8, lost+found:2004, depth:1000m
• location: Red Sea, close to airport Sharm El Sheikh (Egypt)
I was unable to find sonar images. "Deep Ocean Search" participated again [source], assumingly using sonar.

You seem to have done more research on this than most. I.e. your "question" reads more like an answer! ;) I'd almost consider editing to ask a much simplified question, then provide the ones you have researched as an answer to stimulate other competing answers. Just a thought, because it doesn't seem likely that many others here will have done as much work as you already have...

Deep Sea Vision, an ocean exploration company, says it may have found Amelia Earhart's plane:

« By using sonar imaging, a tool for mapping the ocean floor that uses sound waves to measure the distance from the seabed to the
surface, the group has spotted an anomaly in the Pacific Ocean — more
than 16,000 feet (4,877 meters) underwater — that resembles a small
aircraft. The team believes that anomaly could be a Lockheed 10-E
Electra, the 10-passenger plane that Earhart was piloting when she
went missing while attempting to fly around the world. » source: CNN

Thank you for your answer. I have updated the question to exclude speculated crash sites. I had not thought about this possibility.

Note the anomaly was discovered by chance while analyzing data on the ground. Whether it's a plane and it's Earhart's plane needs to be confirmed by going back to the site (undisclosed location) and actually exploring it, as the article says.


text:
Can autothrottle be used without autopilot (and vice versa)?
In commercial passenger aircraft:
Can autothrust be used with A/P disabled ?
And can A/P be used without using autothrust?
Citable references very welcome!
If the question depends on a specific aircraft type, then please B777.

They can be used individually, yes. When flight directors (or autopilot) are on then they dictate what auto throttle should do. But it's not a good idea to fly manually, use auto throttle and have flight directors still on and here is why:

When autopilot is off but the flight directors are on and auto throttle is on you can select a vertical mode like flight level change or vnav and then auto throttle will take commands from that selected vertical mode. In flight level change, for example, thrust is either full climb thrust or idle thrust, which means: If you as a pilot flying don't pitch for speed then you just have throttle stuck in either full or idle and you either overspeed or stall. Not a good idea to leave flight directors on and use autothrottle on its own!
When autopilot is on but auto throttle is off then autopilot and you select a vertical mode like vnav or flight level change then you are in command of delivering thrust, so you need to advance throttle to start climbing or you need to retard throttle to descent. And if you use vertical speed mode you are in control of airspeed. So you have to monitor your climbs and descends and airspeed but it's not too bad. In the end there are other aircraft types that have an autopilot but no auto throttle.
When autopilot is not engaged and flight directors are off then auto throttle controls just speed, this is safe. Airbus' landing checklist has an item for this: "auto thrust? - SPEED".

This applies to 777, 747, 737, A320, A380 and probably (have not checked the fcoms) A350, A330, A340, 757, 767

Yes it can. Autothrottle on most large aircraft (including 777) is considered a separate system from autopilot. To that end, the modules/boxes that control the autothrottle and autopilot are separate as well. This adds a bit of redundancy in that losing autopilot doesn’t mean you also lose autothrottle and vice versa.
Edit: I couldn’t find a clear system data reference to show how the integration of the two systems can be split and/or combined. As was pointed out in the comments, there are multiple sources of information showing this is possible. One such example is this excellent depiction of the FBW (fly-by-wire) systems on the 777. In there, the language alludes to the concept of the autopilot and autothrottle being able to be independently engaged, emphasis mine:

Disarming the Autothrottles through the AT disarm switches on the Mode Control Panel (MCP) will prevent them from "waking-up" at low airspeeds. In such a case the Autopilot, if engaged, will give up on maintaining level altitude and let the aircraft descend in an attempt not to exceed a given angle of attack. An aural and visual warning will alert the pilots of this.

thank you. I doubt neither the veracity of your statement nor your proficiency (as evidenced by having marked your question as helpful answer), but would you have have any references I could cite ?

I do, but I’m speaking from a maintenance perspective and those manuals are generally considered Boeing proprietary info. Let me see if I can find something publicly available to show what’s going on behind the scenes. Flight manuals generally do not go into this level of detail. Please standby.

thank you ... will stand by

With the B777, it is normal procedure to use the autothrottle with A/P off. Normal  takesoffs and landings are done with the autothrottle on and  the A/P off.

@Frank: thank you. Judging from your answer, both systems are independent from each other, meaning the opposite case (using autopilot without autothrust) would be also possible, right? I'm asking because there are cases, where you can use A without B, but not B without A. I have edited my question accordingly.


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Why does the cabin air sometimes smell of kerosene?
Why does the cabin air sometimes smell of jet fuel, although bleed air is tapped before it comes in contact with fuel ? How is this possible?
I have smelled this a couple of times in my life (twice extremely irritating), mostly during boarding/taxiing but at least once also during the flight (although in that case I don't remember if the smell was already present before take-off and merely lingered on).
Apparently a similar observation was reported in Q25405 but limited to the taxiing phase, whereas I witnessed the smell when the plane was still connected to the PBB (and also in-flight with the caveat above). The root cause may differ.

EDIT:
Meanwhile, I have found a satisfying answer on the net, but cannot add it anymore since the question is closed:

« You’ll occasionally notice a strong odor when the plane is on the
  ground – a pungent smell similar to the exhaust from an old car or bus
  that fills the cabin shortly after pushback. Usually this happens when
  exhaust gases are drawn into the air conditioning packs during engine
  start. The wind is often to blame, causing air to backflow or blowing
  fumes through the pack inlets. It normally lasts only a minute or so,
  until the engine is running and stabilized. It’s unpleasant but little
  different from the fumes you occasionally breathe in your car while
  stuck in traffic. » (source)

(Notice that in my cases it lasted definitely much longer than "only a minute or so".)

In my little plane I smell it all the time when taxiing behind a Jet-A burner and sometimes on landing and takeoff. But my aircraft isn’t sealed and pressurized. I suspect what you smell is from fresh air being circulated through the cabin and it picks up some kerosene smell from aircraft around you.

I read elsewhere that once the engines are running, the exhaustion gases can be sucked in again as part of bleed air coming into the cabin. I think from what I've heard so far, this would be the most probable cause. Given that the aircraft is motionless at that point, the fumes will be around the aircraft.

@JScarry: Are you sure that a passenger airliner is "sealed" ? I don't think the fumes came fleeting from elsewhere as there was no aircraft in the immediate vicinity at the gate and the smell stayed for an extended time.

@summerrain They are not completely airtight but unlike little airplanes, they are pressurized so that the air inside doesn’t leak out the doors and windows and conversely the air outside doesn’t leak into the cabin. The air inside the cabin is being constantly recirculated and some outside air is let into the cabin. This article explains how it works. https://aviation.stackexchange.com/questions/43702/how-much-air-is-recirculated-vs-bleed-air-injected-in-modern-airliners-cabin

@JScarry: Isn't "the air outside doesn't leak into the cabin" contradicted by "some outside air is let into the cabin" ?

@JScarry: re: "they are pressurized" - are you saying that the pressure in the cabin on the ground (at the gate) is higher than outside the plane ?

You might have been smelling cooked turbo oil.  Leaking seals can potentially allow oil traces into the compressor bleed discharge, especially on auxiliary power units.  The other possibility is cooked deicing fluid, which is quite common.
Turbo oil and deicing fluid are the two major sources of petrochemical cabin stink.
Another possibility would be an APU with stalling/surging problems where there can be backflow into the compressor end of the motor from the burner can, which will admit burner can gasses into the air conditioning system.  If it is really kerosene you are smelling, that is the probable source.
It could be coming from the main engine but there would likely have been audible rumbling or thumping sounds if it was stalling/surging while on main engine bleed.

If your main engine is stalling/surging you've got bigger problems than a kerosene smell!

If you're smelling it on the ground, it's because there's kerosene in the air around an airport and the plane's door(s) are open. Anything on the wind will blow in. If you don't notice the smell until you're taxiing, remember that the cabin air is recycled by using outside air bled through the engine compressor stages. If you happen to be 6th in a line of aircraft taxiing to the take off end of the runway, there's a lot of burnt kerosene headed your way for the engines to ingest & blow into the cabin of your plane.
If you're smelling it in the air, it's likely that the smell was there on the ground and you just didn't notice and the air inside the cabin hasn't been fully replaced yet.
If the airport is downwind from a paper manufacturing plant, you'll probably never notice the kerosene smell because the paper plant smell would totally overwhelm it, but it would prompt questions of "I was flying out of PAPR and the air smelled really bad, what happened at the airport to cause this?"

re: "there's kerosene in the air around an airport and the plane's door(s) are open" no, the doors were closed. The only open door was connected to the PBB. There were no other planes in the immediate vicinity. re: "you just didn't notice" no, this is impossible not to notice, it's very irritating. But as I wrote in my question it's possible that it already started on the ground.

@summerrain During the pax unloading/loading process, there is at least one pax door open for you to use, and there will almost always be at least one other cabin door open for the maintenance crews, and there will be one or more cargo doors open. None of these doors are weather sealed when opened on the ground for access, and all will allow ambient air into the cabin.

so in short: enjoy your cancer :/


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If all passengers moved to the back, front or one side, would they crash the plane?
all-time classic:
Would the load shift of all passengers herding at the back, front or one side make the plane hard or even impossible to keep in the air ?
Are there any passenger aircraft where this could be a problem ?

scope: Q2507 is about unspecified movement of some passengers ("passengers moving around"). This would hardly be a problem. The scenario presented in this question here is an entirely different one, viz a hypothetical extreme case where ALL passengers gather in 1 spot at the front or back. Also, it addresses a very famous airline myth, and as such it has a valuable purpose.

This will be a problem on almost every passenger aircraft, or any passenger vehicle in general (air, water, ground, underwater, orbital, etc).

Yes, the question is useful. But it's already been answered. There's no point answering it again, because that just fragments the answers and makes them harder to find.

The issue at hand is known as weight and balance. Most of the larger airliners do not have much of a problem with a large shift in Passenger weight but shifting cargo has indeed caused accidents (See https://en.wikipedia.org/wiki/National_Airlines_Flight_102) which was what happened when a large amount of cargo, not properly secured, fell towards the back of the aircraft during takeoff causing the B747 to crash.
In general, the smaller the aircraft, the more sensitive it is to Moment and Arm changes in its weight and balance. If there is too much weight towards the rear (known as Aft-CG) then the pilot may not have enough down-elevator authority to keep the aircraft from pitching up even further.
A forward-CG problem may also happen where there is too much weight towards the front of the aircraft which may cause the pilot to run out of UP elevator authority during the landing flare, causing a nose-first landing.
Both fore and aft Center-of-gravity issues have caused airline crashes in the past although usually not from passengers but rather shifting cargo not properly secured.
I am not aware of any sideways loading issues that could not be corrected with aileron (assuming both wings are attached). Flying with more fuel in one wing than the other can be tiresome but is usually safe.

So what's the answer to "Would the load shift of all passengers herding at the back or front make the plane hard or even impossible to keep in the air ?" (omitting "one 1 side" since you answered that)

Individual passengers moving on a large aircraft is obviously not a problem since there will still be roughly as many in front and back on average, but I'd think that 100+ passengers all moving forward or aft in unison could have as significant an effect as cargo shifting.  Flight attendants move passengers around (often concentrating them over the wings) on empty flights, so it must matter, but is it dangerous or just annoying?


text:
Can ATC handle a flight as emergency although the pilots have not declared an emergency?
The preliminary report for the LNI610 crash shows how much distractive conversation there was between ATC and LIN610 at a time when the pilots clearly didn't have the aircraft under control – as evidenced by the FDR data – and should have talked to each other to diagnose the problem, rather than to ATC. This violates the principle "aviate - navigate - communicate".
While it clearly falls within the responsibility of the crew to declare an emergency, my question is posed from the point of view of air traffic control:
(from the preliminary report, p.1+2)

At 23:21:53 UTC, the LNI610 SIC requested approval to the TE controller “to some holding point”. The TE controller asked the LNI610 the problem of the aircraft and the pilot responded “flight control problem”.
At 23:24:51 UTC, the TE controller added “FLIGHT CONT TROB” text for LNI610
  target label on the controller radar system as reminder that the flight was
  experiencing flight control problem.

The preliminary report reveals how much dispensable talk there was between ATC and LNI610 in this crucial moments even after the flight was marked as experiencing flight control problems.
My question is:
Seeing that the flight was marked by ATC as "FLIGHT CONT TROB", could ATC have handled the situation differently, e.g. bothering them less or even handling the situation outright as PAN PAN (don't restrict navigation, reroute other traffic, avoid communication as much as possible) even though it was not declared as such by the crew ?
Or did they essentially have their hands tied, obliged to treat the flight as any other as long as no emergency is officially declared via either MAYDAY or PAN PAN ?
I very much welcome any answers, including from pilots or ATC controllers who are unfamiliar with this particular accident, but can share their work experience (how this is handled in practice) AND/OR point to specific rules (how this should be handled in theory).

FDR data (timestamps + pink vertical lines added by myself at 23:21:53 and 23:24:51 UTC corresponding to the ATC excerpts quoted above):

In the US, a controller has the authority to treat any situation as an emergency, and they do.  I have had controllers "declare" an emergency multiple times, even when I thought I did not have an emergency.
There are some advantages to the controller.  His work gets shed to others, and his supervisor is at his side to assist.
At one point, after ice, delays and trying to get into a DC airport close to the Christmas holiday, I declared "minimum fuel" which I didn't consider an emergency.  I just wanted to let the controller know that if they vectored me towards West Virginia again, I would be landing close to or at reserves.  The weather at the destination was far better than the ice I have been flying through at 13,000, but I wanted to avoid plunking down at Martinsburg, away from my destination to buy another load of fuel.
Immediately I got handed off to a Dulles controller, whose radar had better coverage than Baltimore Approach who handled approaches normally for my destination.  I got kid glove treatment, and did not get further delays, and landed at my destination without any incident.  After the paperwork, I dipped the tanks, and figured I still had about 27 minutes more fuel than my minimums for IFR night flight with a diversion to better weather.
Similarly, having gear problems almost always gets an "emergency" status.
I will say one thing, when I was dealing with a cockpit fire, and the controller kept asking again and again the same questions it was distracting, but they are trying to get their job done the best as they can, just as the pilot is.  In my case, I just stopped answering lower priority questions.  In the case of the cockpit fire, I killed the master switch (at night), and another pilot in the back brought ATC up on his handheld radio.  Up front we dealt with the fire, and delegated the communications to a guy in back.
So in application to the LNI610 and other situations, it makes sense that the pilots exercise their ability to tell a controller to "standby."  It works some of the time.
I am not as familiar with the US Controllers Handbook as I have been in the past, but I am confident that the controllers have authority to declare an emergency.  But keep in mind that they are products of their environment, just as pilots are, and they have training, objectives, experiences and organizational expectations which change and vary.

Declaring an emergency, especially when fuel is involved, was a factor in the crash of Avianca Flight 52 in January 1990. Not the only factor, but enough for controllers to be more willing to instigate an emergency.

I was in an aviation college back in the 90s; a retired AT controller was our instructor. In the first class we role-played a scenario as ATC with bad weather rolling in and GA aircraft (explicitly not in emergencies) and other aircraft. We decided to land the GA aircraft first. He told us we would have lost our jobs, and that the pilots needed to declare emergencies. (There was probably more to the scenario but details escape me) Was he wrong or did that change over the years?

@Tim, I can't say exactly what your instructor was referring to.  I know that controllers say they handle traffic "first come first serve" but I also know there is a strong bias for commercial carriers.  That is what caused my "minimum fuel" advisory I mentioned in the answer.  I had already had two hours of delaying vectors so 121 carriers could get on the ground. If there is a squall line moving in, and one is bouncing around in a C150, and the controllers are telling you to standby, you should consider the appropriate action for your situation, and do it.

Yes. For example, in the US (I don't know what procedures are used in Indonesia), controllers are instructed (see 10-1-1):

If  the  words  “Mayday”  or  “Pan-Pan”  are  not
  used and you are in doubt that a situation constitutes
  an  emergency  or  potential  emergency,  handle  it  as
  though it were an emergency.
Because  of  the  infinite  variety  of  possible
  emergency situations, specific procedures cannot be
  prescribed.  However,  when  you  believe  an  emergency  exists  or  is  imminent,  select  and  pursue  a
  course of action which appears to be most appropriate
  under  the  circumstances  and  which  most  nearly
  conforms to the instructions in this manual.

In other words, if you think there could be an emergency or potential emergency, use your judgement to handle it appropriately, regardless of which words are used. The controller's hands are not tied by the failure to use the magic words "PAN PAN" and or "MAYDAY."
Controllers aren't mind readers though, and don't inherently know what an aircraft in distress needs unless that's communicated. "Flight control problem" encompasses a pretty wide range of conditions, and since the crew asked to proceed to "some holding point," it could be reasonable for the controller to conclude that the situation was stable until the crew stated their intentions. Whether the controller's communications interfered with the crew's ability to address the problem is something that could be addressed in the investigation's final report, along with recommendations to improve ATC procedures in the future.

The job of ATC is to help the pilots get where they need to go safely and efficiently. In order to do that, they have to ask questions, to know what emergency services need to be alerted or where the airplane might be able to land if needed.
The mantra of pilots is aviate, navigate, communicate. Communication comes last. If they are saturated with the most important items (flying and navigating), they are trained to worry less about communicating. Unless ATC has something more important to add, they can wait. The systems is already designed to handle communication failures, even if inadvertent. ATC can always clear other aircraft out of the way if they have to. If an airplane says they have flight control issues, and begins flying erratically, you can be sure that's their first priority.
ATC does not have to have a formal declaration of emergency to change the way they are handling traffic. Sometimes they can tell something is wrong and they do all they can to help. But they can't know everything. If a plane is having issues, it's the pilot's job to deal with that and let ATC know what they need.

The flight controller typically has full authority to conduct traffic in a safe manner. If they felt they had to redirect traffic, allow the aircraft to travel unrestricted, or reduce the amount of communication, it's within their power to do that - of course, they may be questioned after the fact whether it was necessary, but they certainly have the right to make those decisions. However, a controller cannot officially declare an emergency for the aircraft, as that decision can only be made by the flight crew (more specifically, the captain would be the authority on whether it is an emergency.
In the case of Lion Air 610, the pilots did indeed say they were having trouble with their flight controls, however the information they transmitted to the controllers would not constitute an emergency alone. Non-critical issues with flight controls are somewhat common, and typically they would return to land under normal procedure to be checked out by mechanics. 610's total loss of control happened fairly suddenly, though there was partial/temporary loss leading up to it.

Video at 12:17 of ATC declaring an emergency for an aircraft.

Short answer - YES.
Long answer -
Back in about 1995, I was working the airspace around eastern Wyoming and western Nebraska, when Casper FSS (located at Casper, back then) called me about a lost aircraft on their frequency. After a couple of minutes of sorting out reversed position reports (pilot was giving the wrong radial from the NAVAID), I established that the aircraft was 70 miles NE of KGCC (Gillette, Wyoming). He was trying to go to GCC, VFR. He was not IFR qualified.
I gave him a code, got him in radar, and asked if he was IFR qualified. "No", he answered...
KGCC was low IFR, with 1/4 mile visibility, so I asked his intentions. "Well, we want to land at KGCC", was his response. I informed him that the weather was below IFR minima for all approaches.
When I asked his flight conditions, he told me he was in the clouds... NOT a good answer.
At this point, I informed my supervisor that I was declaring an emergency on the pilot's behalf.
I did not inform the pilot. No need to upset him.
I informed him that I was giving him a clearance, and he needed to do what I told him. He agreed. I put the aircraft on a 150 heading, toward CDR (Chadron, NE), which was reporting VFR. I had him put the aircraft at FL090, so I could keep him in radar.
After a couple of minutes handling other aircraft, I looked, and the guy had disappeared. I asked where he was, and he said, "Oh, we saw a hole in the clouds, and dropped beneath them, and now we're heading back up to KGCC". I then told him he was to get the aircraft back to 9000 feet (FL090), and expect turns back to KCDR. He didn't like it, but he did as he was told.
As he approached CDR, the weather began to go down, so the fellow that relieved me gave the pilot a vector to KBFF, where he landed safely. We got word to his family, who were waiting at GCC, that he was OK.
He called a couple of days later and thanked us.

Sometimes pilots are reluctant to declare emergency for different reasons( media, Inspection,..).even in a real emergency some pilots do not use related phraseology to convey the state of the flight. Controllers should be trained to resolve any confusion in communications resulted from several factors such as sociocultural and cognitive effects , in these cases controllers may need to take necessary actions to handle the flight like an emergency from a flight safety standpoint.  Controllers may declare emergency for the pilots if situations entail that and there were some cases in which controllers for example observed fire in the planes but  were denied by the pilots and subsequently controllers declared emergency and saved the flights. Moreover according to a research conducted by Immanuel Barshi , A NASA scientist and pilot, controllers can declare emergency for the flights if necessary. Remember that an urgency may lead to an emergency, so a prior preparedness to handle the situation if required can save the time and lives.of course there is no "one size fit all" rule and every situation may implicate a separate course of action.

To „declare an emergency“ is also really a US only thing. Over here in europe there‘s no difference if you say „engine no. 4 failure, declaring an emergency“ or „engine no. 4 failure, no emergency“. We will treat you the exact same way as internally you will be an emergency. And if we need you on squawk 7700 to make life easier - that’s how it is

It is wise that controllers alert even when the pilot has not declared an emergency. They have to be prepared and start coordination and assessment of the situation because one situation that is not emergent in the air can turn quickly to a distress one. This does not mean that controllers have to block the frequency and ask every moment. The controllers rule is ASSIST:

Acknowledge the call; get the squawk
Separate the aircraft from other traffic. Give it room to manoeuvre
Silence - on the frequency. Provide separate frequency where possible - this prevents unnecessary clutter for the pilots
Inform those who need to know and those who can help; inform others as appropriate
Support the pilots in any way possible - Start to think of alternative routings, etc.
Time - Give the pilots time to collect their thoughts, don’t harass them for information. Time produces good decisions

So at some situations they have to be silent. The problem of declaring or not the emergency by the pilots sometimes is that some of them are reluctant to declare at once for being extra charged by some airports.


text:
Which of the pilots flies when it gets dangerous?
Who flies when it gets dangerous ?
In other words: Which pilot takes control of a passenger aircraft as Pilot Flying (PF) in an emergency (aircraft upset, loss of control, mechanical failure, etc.) and why ?

the highest-ranking pilot present in the cockpit given his experience
the SIC (second in command), for the reasons quoted below
whoever was PF when the incident began continues flying
or no specific rules, the pilots must make a joint decision

Just beware that either pilot may be at the controls during a
  particular incident. In fact, while protocols are different [from] carrier to
  carrier, it's not unusual during emergencies or other abnormal
  situations, for the captain to delegate hands-on flying duties to the
  copilot, so that the captain can concentrate on communications,
  troubleshooting, coordinating the checklists, etc. (source)

Case in point:
In the AF447 crash, the captain was not in the cockpit when the incident began. When returning to the cockpit, he did not take over control but sat down behind the 2 First Officers.

Please mention in your answer
- which person (if any) is designated by the regulations, airline rules and best practices
- for what reason
- and whether these rules/recommendations have often been not followed in crashes

Possible duplicate of Who has the authority between captain and first officer in emergencies?

@fooot: No. These are 2 entirely separate questions. The other question asks who is in charge. My question asks who flies. (The pilot in command is not necessarily the one flying, as can be seen in my quote). Please remove the dupe-tag.

By way of example, the BA Flight 38 crash saw the co-pilot maintain control all the way to impact while the Captain took the decision to change the flaps, attempt an APU start and get a Mayday out

@fooot: The Captain doesn't have to be PF. He can choose to be PM and still have authority.

And it's up to the crew to coordinate who is PF just as with who is PIC.

@fooot: My question asks who flies (who is PF). Other question asks who is in charge. These are separate questions. Please remove the dupe flag.

Too many acronyms!  What is PF?  What is PM?

@StuSmith: wiki, skybrary

In the end it's all up to the Captain.  If the FO is PF, which with most airlines alternates with each leg of a block, and something exciting happens, the capt may let the FO continue flying if the capt feels the FO has things under control.  Or the capt may say "I have control" and take over.  Depends.
The Pilot In Command is pilot in command.  He/she commands, but with modern CRM rules, there is expected to be some mutual consultation and decision making, so the command authority has to take all that into account.
AF447 was an unusual situation where the capt didn't realize early enough what a clusterfark the two FOs sitting in the front seats had gotten themselves into, who were both mentally overloaded into a tunnel vision state, and especially the right seater, who appeared to lack basic fully internalized flying skills, sitting in panic mode with the stick full aft for almost the entire ride down.


text:
co-pilot incapacitation: land alone or with a passenger-pilot?
Pilots are trained to safely fly the aircraft in case of co-pilot incapacitation:

"A commercial aircraft can be landed with one pilot at the control and
  Delta pilots are fully trained to do so if the situation were to
  occur." (Delta representative)

FAA AC 25.1523-1 requires all aircraft to be capable of operation
  by one pilot only from either seat, so just one pilot can safely fly
  the aircraft - albeit under increased workload. (source)

So why would a pilot in such a situation elect to ask over the PA system "are there any non-revenue pilots on board, please ring your call button" and then land the plane together with this unknown person (a military pilot in this case) ?
This happened on United Airlines Flight 1637. Sure, if it turns out right (which it did in this case), it's certainly pleasant to have a helping hand. But there are all sort of things which could go wrong (“At the beginning, I interrupted her flow of operations, but we figured everything out extremely quickly."). Personally, I'd much rather prefer not being interrupted and distracted when I have to concentrate in this critical moment. Why take any risk at all when one pilot should be able to safely land alone?

There are risks either case. There are no hard rules for or against calling a pilot from the cabin for help; it is up to the pilot to evaluate the situation and select the best course of action.
The risk of landing solo is greatly increased workload, which increases the chances of human error. There are quite a few things to attend to when flying an airliner (compared to a small aircraft). It gets worse when you're in busy airspace.
The risk of asking someone to help is the uncertainly of whether this person will do more harm than good. There would be differences in flight experience and operation procedures. However, Crew Resource Management and handling ATC radio applies to pretty much all types of flying.
Historically there had been examples of either choice, and they both turned out fine.

It's not all that bad in the first place.  In an IC situation, once the emergency is declared, ATC clears the decks for you and does whatever it has to do to accommodate you, so you end up with the luxury of a lot more time to set up an arrival by yourself than you would in a normal situation setting up and flying a STAR in a chain of aircraft and you have to get it all done go go go no screw ups.  And the other thing is, jets are actually really easy to fly once you have adapted to their space/time environment, easier than a lot of light aircraft and turboprops.  The demands are all mental.

I agree with @JohnK -- the workload wouldn't be all that bad, and ATC would simplify things as much as possible. Personally, if I had one of our pilots in that back, I'd have the flight attendants bring him up. But if it's not "one of us" then I wouldn't... what a pilot who doesn't know our procedures (or worse, our aircraft & FMC) can do, I don't need. He'd be a distraction more than a help. OTOH, if I also "had the fish" and thought I might be heading toward incapacitation as well, that's a whole different story.

An unexpected emergency landing at an unfamiliar airport is stressful enough with two pilots; doing it alone would be much worse. There is a very good argument for having an extra set of eyes, ears and hands to take the easier things off your plate so you can focus on the hard ones. But trusting a random stranger to jump in mid-air wouldn't be an easy call.

It it was me I'd have someone brought up just to work the gear and flap levers for me, so I didn't have to reach over the centre console, but nothing else.  If the airplane itself has nothing wrong with it, a landing on a runway is a landing on a runway.  The biggest mental demand for NORMAL operations (nothing wrong with the plane itself) is mastering the FMS.  If you're a whiz on the FMS (and you should be), and you have the autopilot to do 95% of the flying for you, it's not difficult, except to the extent that an inexperienced FO would be stressed and intimidated by being alone.

I've heard people say that their airline SOP was to have a FA sit in the jumpseat just to help read of checklists.

@JohnK “ATC clears the decks for you and does whatever it has to do to accommodate you”… unless you run into a particularly obnoxious controller like is this incident: https://youtu.be/aug1mORZKUE (I believe and hope it is a really rare case).


text:
Is the bleed air passengers breathe tapped from the engines before or after it comes in contact with fuel? And why? Isn't this unhealthy?
Passengers are often surprised to hear that the air they breathe comes from inside the engines.

This sounds unhealthy. Can you explain, why it is not ?
Is bleed air tapped (for cabin pressurization) before or after it comes in contact with fuel inside turbofan engines on passenger airliners ?
And what is the reason for either choice ?
Specifically where is the location in this diagram ? (diagrams in answers would be very welcome)

scope: This question is about the air breathed by humans inside the plane. Q11917 is about de-icing. Neither the question nor the answers in Q11917 deal with the aspect of whether the air would be safely breathable for passengers and crew. This aspect is very well dealt with in the comments and answers below. As such, these questions should remain separate.

Think about this for a second - if it comes after the air is in contact with the fuel and it's being used for cabin pressurization, that would mean you'd be building up a fuel-air mixture in the cabin - which would be toxic in the best scenario, and explosive in the worst.

I'm asking because cabin air sometimes smells of kerosene.

I'd guess cabin air smelling of kerosene has to do with standing on the ground before takeoff amid kerosene being used --- by other planes, by own idling engines, wafting from just-released fuel truck nozzle, ...  --- so whatever outside air is taken in must carry the smell (via the open doors everyone just entered through, if from a staircase;  or any air intake point).

Possible duplicate of Why is bleed air taken from some stage of the compressor used for de-icing? Why not e.g. exhaust gas?

clarified the difference

@fooot I don't see how it's a duplicate of that. Cabin air isn't taken from the exhaust because the passengers need oxygen; it isn't taken after fuel injection because the passengers need a cabin full of no jet fuel.

The bleed will be tapped from one or two of the 3rd, 4th, 5th or 6th High Pressure Compressor stages.  Usually there are two bleed ports.  The highest pressure port will supply really hot air for things like anti-icing.  The lower pressure port farther upstream will supply air for air conditioning/pressurization and other pneumatics.  Some systems combine the two ports into one system and draw from the low pressure or high pressure one as required.
The air has to come from the compressor, not after combustion, mainly because it needs to be clean ambient air free of kerosene combustion byproducts, and it's plenty hot enough anyway and taking it from the turbine would be way too hot.  The discharge in the last stages of the HP compressor can be upwards of 700-800F at takeoff thrust.
If the aircraft uses a high temperature "evaporative" anti-icing system, it will tap air from hotter stages of the compressor than if there is a non-evaporative system (Evaporative = anti-iced skin temperatures above the boiling point of water.  The leading edge will be over 100 C, like the surface of a steam iron.)
Even if it is taking "clean" air, the bleed flow will have all sorts of charred bits of things from the atmosphere in it; pollen, bits of bugs, that collect and get everything dirty in the ducting and components (at lower altitudes).  Combusted air would be ten times worse, not to mention the carbon monoxide poisoning the passengers and being way too hot to be usable in the first place.

7th stage bleed is also possible on some engines.

Anti-deicing sounds like a terrorist plot :-0

A secondary reason for multiple bleed ports is to keep the compressor stable. Unlike turbines, compressors are potentially unstable devices, and the overall flow conditions need to be controlled to avoid stall or surge. The bleed ports are in effect part of that control system.

Just about all modern jets have variable stator vanes for that purpose and don't need to dump bleed air overboard to control compressor flow.   The amount of bleed demand is a function of the demand of the services using it.  When you turn packs on or anti-ice on you get an ITT rise and if you turn them off the ITT goes back down.  If bleeds are turned off they are off.

"not to mention the carbon monoxide poisoning the passengers" let's not quibble over small details :-)

I would hope that passenger airliner engines achieve complete combustion of the fuel, which would mean carbon dioxide poisoning, not monoxide. Not that this difference would matter much. :-D

@DevSolar "Clean" from the perspective of a massive jet engine differs quite a bit from "clean" from the perspective of our fragile little human lungs. Even if the combustion is almost perfectly complete, the sheer amount going on would quickly bring ambient CO to lethal concentrations.

I have found a diagram (bbc.com) showing the location where the bleed air is tapped (red arrow).
As can be seen in the image, the location is upstream of the combustion chambers, which means that bleed air is tapped before it comes into contact with fuel:

I am late to the party, but
Is it possible that some combustion/combusted particle are trapped in the system at landing, when thrust reversal is applied?
That would explain the persistent smell of kerosene at take off .. air with fuel particles being pushed in the cabin at restart.

@EarlGrey: On airliners, reversers are not on the core flow feeding the combustors, but on the bypass flow. Reversed air flow just comes from the fan and is never in contact with the actual engine, fuel or combustion gas and it is not used as bleed air anyway. See this question. On the other hand sometimes air is reversed in the hot flow, that's called a compressor surge, and in that case gas might enter the cabin through the compressor bleed air tapping points.

From this answer, on the B737NG bleed air tap point:

Compressed air is tapped from the engine 5th and/or 9th compressor stage. Air supply is regulated according to demand and varies according to flight stage - during flight stages with relatively high engine power (take-off, climb, most cruise), 5th stage compressed air only is used. During low engine power conditions such as approach and landing, 9th stage compressed air is used for the pneumatic systems as well. This air is under higher pressure, and hotter, than the 5th stage air.

So bleed air for the air conditioning system is tapped before any fuel enters into the picture. Obviously. The cabin sometimes smelling of kerosene or of jet fuel exhaust when on the tarmac is usually related to external circumstances, such as a tail wind, as per @Dave's answer.
As mentioned by @mins in a comment, there has been research into the cause of some episodes of pilot intoxication from conditioned air, which turned out to be from the engine sump oil.

I know you know it, but for visitors, it's worth saying the problem with bleed air is not from fuel (except maybe in case of compressor stall/surge) but from lubricant fumes from the sump entering the compressor. Someone did a full study of this aspect.

To add to what John K already posted, cooling requirements prevent any bleed air being taken in the combustor and high pressure turbine sections. In these sections, thin film cooling is preformed where a small amount of air is injected around the surfaces to prevent the hot combustion products from touching them. Even if the bleed air was being taken for a non-human contact purpose such as active flow control, the air is simply too hot to handle at this point.


text:
Do pilots get more fresh air than passengers?
There is a famous air travel myth claiming that "pilots get more fresh air than passengers".

       (source: The pure cure, p.375)

I would like experts to either dispel or confirm this myth, that pilots receive "better air" with higher oxygen levels than passengers, who have to breathe more recirculated air.
Although at first glance it might sound absurd, but when you think about it, it would actually make sense, because:

The worst thing that can happen to passengers is that they get tired. Sure, that may be unpleasant (think of the stale air in a crowded room), but does not pose a health or security risk.
Pilots, on the other hand, need to be wide awake and perform to the top of their abilities, as errors can be fatal. So any negative outside influences on pilot performance needs to be eliminated. In particular, pilot fatigue significantly increases the risk of pilot error.

However "CO2 levels directly affect pilots’ flight performance" as was tested in a study on 30 active commercial airline pilots performing maneuvers under varying carbon dioxide concentrations:

press release
Previous research led by Allen and colleagues found that, in office buildings, CO2 concentrations between 1000-2500 ppm – levels once thought to be benign – negatively impact the cognitive function of employees. For the new study, they wanted to determine if higher CO2 levels on the flight deck would impair a pilot’s ability to perform advanced maneuvers and manage emergency situations, such as a single-engine failure during takeoff. […] Average CO2 levels on the flight deck are less than 800 ppm. However, they have been measured as high as 2000 ppm on the flight deck and even higher in the cabin during the boarding process. […] The National Research Council has suggested that current standards for ventilation rates on flight decks may be inadequate.
background
  On the flight deck […] the average CO2 concentrations are typically <1000 ppm, but the 95th percentile concentration can be as high as 1400 ppm, depending on airplane type.
results
  Compared to segments at a CO2 concentration of 2500 ppm, the
  odds of passing a maneuver as rated by the Examiner in the simulator
  were 1.52 times higher when pilots were exposed to
  1500 ppm and 1.69 times higher when exposed to 700 ppm.

In light of the above it would make sense to prioritize pilots over passengers when it comes to circulation of fresh air.

I will post the results of my research into this question as an answer below, but would welcome other answers presenting technical evidence and quoting citable references.

scope:
This is not the same question as Q57941.
Q57941 asks if there is airflow between cockpit and cabin (as opposed to be hermetically sealed).
Whereas this question asks if more fresh air from OUTSIDE flows into the cockpit than into the cabin. Also, it addresses a very famous airline myth, and as such it has a valuable purpose.

Related: Do pilots breathe the same air as passengers?(

The statement that pilots can get 10x more oxygen than pax, on its own, does not make sense.  A 10x difference would either mean the pilots are breathing 100% $O_2$, which is just not necessary, or the passengers are beginning to die.  The only extenuating case where it might be true is during an emergency descent where the oxygen masks have dropped, and only long enough to get down to 10,000 ft.

@abelenky: You are talking about a 10x higher oxygen concentration in the air. I don't think this is the claim, but rather 10x higher airflow (and thus oxygen flow) per person, e.g. 10 CFMP (ft³/min per person) in the cabin and 100 CFMP in the cockpit.

Note in particular that while this has an alleged endnote citation, Ms. Fairechild is not actually quoted but paraphrased.

@summerrain If that's what they meant to claim, then saying "ten times more oxygen" is a really strange way to say it. I was thinking the same thing as abelensky when I read that.

Flight attendants are not scientists. That's how normal people talk.

Taking the B737 as an example, fresh air from the left pack flows directly into the cockpit (green airflow in the diagram), whereas the passenger cabin is served from the mix manifold only (yellow). Therefore

pilots receive 100% fresh air
while passengers receive a mix of 50% fresh air and 50% re-circulated cabin air on average, across all aircraft types

share of re-circulated air (red) in the cabin ventilation air (yellow):
B737: pilots 0% passengers 25%
B757: pilots 0% passengers 50%
B767: pilots 0% passengers 50%
B777: pilots 0% passengers  ?

In a cabin packed with hundreds of people each transforming 21% O2 and 0.04% CO2 into 16% O2 and 4% CO2 (i.e. breathing) and where 50% of this exhaled used air (red) is recirculated back into the cabin (yellow), O2 and CO2 levels are poorer than in the cockpit not supplied with exhaled used air.

The AFA-CWA flight attendants association indicates how much fresh air each person receives:

How much air is supplied in the economy section? 6-10 ft³/min of outside air to each person which is about half what is recommended in
  buildings and transportation vehicles.
The cockpit gets 50-100 ft³/min per person of outside air, or sometimes a mix of outside and recirculated air depending on the
  aircraft type. That is up to 20 times more than in the passenger
  cabin.

It's actually a minority of the left pack air going to the flight deck; maybe a third of so.  The bulk of it is going to the cabin to supplement the right pack, being the less restrictive path.  Not to say the air quality still isn't better up front.

In other words 33% of the fresh air from the left pack is for 2 persons only.

@summerrain the two people are V.I.P.s...

Yeah, insofar as bad air can make you a bit sleepy, I'd much rather doze off in the middle of my book than have the pilot so much as think about needing another coffee.

@Harper. Yes, but the question is not about why they get more fresh air, but do they.

Harper: @Penguin is right. The question lists good reasons for prioritizing the pilots.

I can confirm that similar air distribution systems also exist for:

Boeing 777:

The flight deck receives 100% fresh conditioned air from the left pack. The flight deck is maintained at a slightly higher pressure than the passenger cabin to prevent smoke and objectionable odors from entering the flight deck.

(source: 777-200 FCOMv2 2.20.3 Air Systems - Air Conditioning System Description)
Boeing 747: Pack 1 directly supplies the flight deck:

(source: 747-400 FCOMv2 2.20.4 Air Systems - Air Conditioning System Description)

(source: 747-8 FCOMv2 2.20.5 Air Systems - Air Conditioning System Description)

This is, however, not the case for the following aircraft:

Airbus A320: The mixing unit supplies air to the flight deck and passenger cabin equally:

(source: A320 FCOM 1.21.10 Air Conditioning)

Bombardier Dash-8 Q400:

(source: smartcockpit.com)

In the end it depends on the aircraft type. It seems on Boeing aircraft the flight deck air is indeed fresher than the cabin air because it receives no recirculated air (during normal operations).
However, it is not clear what "ten times more oxygen" is supposed to mean in the article. It certainly does not mean a ten times higher oxygen concentration (as already noted in the comments). A ten times higher flow rate would not impact the available oxygen partial pressure either.

Great answer! – I only disagree with the last sentence. Of course if you are in a cabin packed with hundreds of people all consuming oxygen and exhaling carbon dioxide, and 50% of the exhaled used air is recirculated back into the cabin, then of course the O₂ and CO₂ levels will be poorer than in the cockpit.


text:
How unusual were MH370's final ATC exchanges?
There are 2 noteworthy occurrences in the ATC radio transcript within just minutes of a 3rd noteworthy, quite unprecedented occurrence in aviation history:

At 01:07:55 MH370 unnecessarily reported maintaining FL350 a second time
At 01:19:29 MH370 famously only replied "Good Night, Malaysian 370" without reading back the frequency for the handover, although this is an ATC instruction that should be repeated (see below)
At 01:20:33 MH370 "goes dark" (losing XPNDR, ACARS and SDU).

This temporal proximity caught my attention and left me wondering if the 2 ATC transmissions cited above are out of the ordinary (and thus a possible precursor of what was to come).

background information:

What are some important things controllers usually expect you to read back?
  • Clearances: headings, vectors, altitudes, transponder codes, and radio
  frequencies. (a288)

« The last radio transmission “Good Night Malaysian Three Seven Zero”
  was spoken by the PIC. However, he did not readback the assigned
  frequency, which was inconsistent with radio-telephony procedures. »
  (safety investigation report, p.431)

questions

Please cite what (if any) ATC rules have not been followed.
From your experience as flight controllers or pilots, how unusual is that ? Is this rather unheard of or occurring fairly regularly ?
Is the handoff procedure described below by the 767 Captain technically correct and does the missing step 3 permit the conclusion that step 2 was not executed either ?

@Edward_767, a 767 captain, has closely studied the audio recordings
  of the MH370 radio transmissions. He is convinced that the second
  altitude call at 01:07:55 was NOT made by the Captain, but by the
  First Officer, possibly because the captain was not in the cockpit at
  that time. His theory is that the first officer made the call because
  he was not sure whether the captain had made the previous altitude
  call at 01:01:14.
He makes another interesting observation regarding the final exchange
  where MH370 is handed off to HCM. He states that the typical radio
  procedure would be to

receive the new frequency (in this case, 120.9 MHz)
dial it into the radio as the standby frequency
read back what frequency was dialed in as part of the confirmation of the handoff
listen for the final transmission
hit the radio switch which swaps the active and standby frequencies
and call ATC on the new frequency.

In the transmission that acknowledged the handoff to HCM, the captain
  did not read back the frequency. Ed believes this is because the new
  frequency was never dialed into the radio, as the captain never
  anticipated making a call to HCM ATC. Ed believes the missing
  frequency during the acknowledgement of the handoff is yet another red
  flag.
The time between the 2 transmissions would be less than 15 seconds. It
  was 13 seconds at MH370’s previous controller handoff, where the new
  frequency was read back. At the handoff between Kuala Lumpur and Ho Chi
  Minh, the pilot acknowledged the handoff, but never read back the new
  frequency, and the call to Ho Chi Minh was not made. That leaves a window
  of only about 15 seconds for the abnormal event that caused the turn back.

ATC transmission log (full transcript incl. taxiing here)

I'm borderline on whether to close this question as "primarily opinion-based". Is this covered in the investigation report or should the community answer? My answer is "a bit out of the ordinary but not alarming unusual", but everyone's ATC experience is different.

I think this is opinion based @kevin. Personally I think that analysis is reaching, the exchange seems pretty normal to me, however I don't think there are good answers. MH370 should have read back the frequency but the fact they didn't means very little to me.

I am not asking for an opinion. The question "was this ATC exchange rude" would be opinion-based. This question, on the other hand, is factual. It asks would rules were violated and asks how often this occurs, which is based on a specific number – just as much as "how often overbooking occurs" is a concrete number. Although the latter is easier to state numerically, approximations can be given for the former. As such it is not opinion-based, but based on experience and a concrete number.

I believe that this question can be answered in satisfactory way without too much opinion. Deviation from standard phraseology and procedures is not good, but it happens all the time. There are certain circumstances where such deviations become the new normal. Somebody could analyse whether this is such a situation and present their findings in an answer.

There might be good answers. Why not give them a chance before closing this question? Don't see why muzzling this is helpful in any way. These were MH370's famous last words, which merit a good analysis. Certainly some ATC controllers would have something to say about this and like to share their experience.

"Deviation from standard phraseology and procedures is not good, but it happens all the time." is in fact a non-opinion-based answer to the question. This should not have been closed on that basis.

I have not heard the actual audio in context; I've only read the transcripts.
However, from the transcripts, I see the timing between some of their calls as a bit confusing and unusual.
01:01:14 | MH370 | Malaysian 3 7 0 maintaining level 3 5 0
This is slightly odd, because 11 minutes earlier they were told to climb to 350.   I do not think it is common to report when you have finished your climb.  ATC can see you leveling off at your assigned altitude.
Because of this unexpected, slightly odd call, ATC responds with:01:01:19 |  ATC  | Malaysian 3 7 0
("You called me.  ATC is here; I hear you loud-and-clear; Go ahead: What is your request?")
There is no response for 6 and a half minutes. This could reasonably be because MH370 has no request, and doesn't need anything from ATC, or perhaps they are having radio difficulty and did not hear ATC's call?  The most extreme interpretation would be that there is currently something happening in the cockpit that is distracting them.  Perhaps a lack of oxygen? Or some other distraction?
After 6 and half minutes, MH370 makes the same call again:
01:07:55 | MH370 | Malaysian...3 7 0 maintaining level 3 5 0
Again, this reads like the preface to a request.  Perhaps they didn't hear ATC last time, and are calling in again with a request? Perhaps they're suffering from hypoxia, and don't even remember that they already reported in?
ATC quickly responds the same way again:
01:08:00 |  ATC  | Malaysian 3 7 0
(I'm still here, I still hear you.  Go ahead with your request.)
Silence again for 11 minutes, before ATC gives them a normal instruction to change to the next frequency.  MH370 responds normally by acknowledging the instruction. At this point, we have confidence that their radio is working, and can probably rule out technical problems for the earlier lack of a request.
Technically, they should read back the frequency, but it is not at all unusual for a pilot to just acknowledge when he is confident he copied it right, such as a crystal clear transmission, or a route he's flown many times and a frequency he knows well.  Or, the lack of confirmation could indicate hypoxia or another mental impairment. Or that he has no intention of copying the frequency or changing to it.
My biggest point of concern and confusion is that MH370 twice reports their altitude, which sounds like they're calling ATC to make a request, and then says nothing more for 6 and 11 minutes.  The significance of this is not at all clear.  Either hypoxia or radio/electrical problems would explain this.  A cockpit struggle does not seem apparent, but some sort of distraction in the cockpit could cause them to start a conversation but never complete it.
My personal opinion, without much supporting evidence, is mental impairment, potentially due to failed pressurization, carbon monoxide, or other contamination like engine-oil in bleed air, which has been known to cause neurological damage.

-1 for the last paragraph. (The rest at least explains what may classify the radio calls being characterized as unusual, and thanks for taking the time to do that).

Though those transmissions are slightly odd, I feel like almost any aviation transcript will have some idiosyncracies that can be made significant with a small amount of peridolia and post-hoc reasoning. Good answer, though.

+1 for your thoughtful, excellent analysis

Agree with @KorvinStarmast, downvoted because of speculations. Besides, reporting reaching a cleared level is completely normal in many parts of the world, especially areas where radar coverage might be limited.

I don't agree that speculations warrant downvotes if they are marked as such and are carefully presented in the form of different and competing possibilities, as is the case here.

Please cite what (if any) ATC rules have not been followed.

No ICAO recommendations were explicitly broken. Whether or not the local authorities require the pilots to read back a newly assigned radio frequency, I do not know, you will need to refer to the local laws to determine that.
It is likely that reading back new radio frequencies is mandatory, but not doing so is not a major violation in any case.

From your experience as flight controllers or pilots, how unusual is that ? Is this rather unheard of or occurring fairly regularly?

Slightly unusual. Pilots will normally read back newly assigned radio frequencies, but every once in a while, for some reason or another, they miss doing so. Typically happens with local pilots who are very familiar with which radio frequencies they expect to use during a flight.
As for the level report ("maintaining level 350"), not unusual at all. Local rules may even require pilots to report reaching a cleared level. Especially in parts of the world where radar coverage is limited (such as over the ocean), pilots are probably used to having to report reaching a cleared level, so they will do it out of habit even if the rules do not require it. The fact that they do it twice? Meh, they probably weren't sure if they had done it already, so opted for the safe choice of doing it again. This is very typical within aviation - if you are unsure, better safe than sorry.

Is the handoff procedure described below by the 767 Captain technically correct and does the missing step 3 permit the conclusion that step 2 was not executed either ?

Yes, the procedure is correct. No, missing step 3 does not permit the conclusion that step 2 was missed.
In conclusion, the radio transmissions you mention are in no way unusual enough to suggest, on their own, that anything was wrong.


text:
Has a passenger or cabin crew member ever flown an airliner?
Is there any documented case, excluding hijacking, where a passenger or cabin crew member had to fly an airliner (hands on yoke/stick) – even if just briefly – due to an emergency (pilot incapacitation being the most likely one) in which he/she had to replace the pilot mid-flight ?
Aside from talk-down aircraft landings of small aircraft and stand-ins as Pilot Monitoring (which are both beyond the scope of this question), the only case I could find is:

Helios Airways Flight 522 where a flight attendant was spotted in the captain's seat shortly before the plane crashed

Do you know any other cases ?
I'm particularly interested in cases, in which the stand-in pilot was unqualified to fly this specific plane, but absent such cases all stand-ins as Pilot Flying in an airliner count.

I think that in United Airlines Flight 232 Dennis E. Fitch did. While flying as a passenger on this flight, he actually was a certified flight instructor for the plane of that type so competent.
Chances to find a type-rated ATP between the passengers who would fly as if nothing may look slim but they are not zero. It is statistically more probable to find a pilot between passengers than would be just by random chance, because of deadheading.

One thing to consider are types that dominate a fleet. For example LCCs like Southwest and Ryanair only fly one type, so any deadheading or nonrev company pilot is qualified to fly. Emirates has 58% 777s, the rest are A380s. Even with United, 44% of their aircraft are 737s.

Yes (well not an emergency), Aeroflot Flight Flight 593 was a fairly famous incident where the pilots son (a passenger on the flight) was in the cockpit and playing with the controls. He accidentally disconnected the autopilot and lead to the aircrafts ultimate crash.

Unlike his sister, Eldar applied enough force to the control column to
  contradict the autopilot for 30 seconds. This caused the flight
  computer to switch the plane's ailerons to manual control while
  maintaining control over the other flight systems. A silent indicator
  light came on to alert the pilots to this partial disengagement. The
  pilots, who had previously flown Russian-designed planes which had
  audible warning signals, apparently failed to notice it.

So he was at the controls for at least 30 seconds.
This question is also related as is this one.

Not exactly what I had in mind, but yes, that counts. Any other ?